Java Oops Concept

Java Oops Concept:

1.       Objects

2.       Class

3.       Inheritance

4.       Polymorphism

5.       Abstraction

6.       Encapsulation

Object :

Any entity that has state and behaviour is known as an Object.

An object can be defined as an instance of a class.

Example :

Object = {property 1: value1, property 2: value 2……property n: value n}

Class :

• Collection of object is called class.
• It is a logical entity
• Class doesn’t consume any space.
• A class can also be defined as a blueprint from which you can create an individual object.

 

 

Inheritance :

When one object acquires all the properties and behaviours of a parent object, it is known as inheritance.

It provides code reusability.

It is a used to achieve runtime polymorphism.

 

Polymorphism :

If one task is performed in different way, it is known as polymorphism.

In java we use method overloading and method overriding.

 

Abstraction :

Hinding internal details and showing functionality is known as abstraction.

 

Encapsulation :

Binding or wrapping code and data together into a single unit are known as encapsulation.

Naming Convention :

1.     Class

    . It should start with the uppercase letter.

  It should be a noun such as Color, Button, System, Thread, etc.
Use appropriate words, instead of acronyms.

Example :

Public class Employee {

//code snippet

}

 

2.     Interface

It should start with the uppercase letter.

It should be an adjective such as Runnable, Remote, ActionListener.

Use appropriate words, instead of acronyms.

 

Example :

 

Interface Printable

{

//code snippet

}

3.     Method

It should start with lowercase letter.
It should be a verb such as main(), print(), println().
If the name contains multiple words, start it with a lowercase letter followed by an uppercase letter such as actionPerformed().

Example :

Class Employee

{

//method

Void get( )

{

//code snippet

}

}

4.     Variables

It should start with a lowercase letter such as id, name.

It should not start with the special characters like & (ampersand), $ (dollar), _ (underscore).

If the name contains multiple words, start it with the lowercase letter followed by an uppercase letter such as firstName, lastName.

Avoid using one-character variables such as x, y, z.

Example :

Class Employee

{

// variables

Int id;

Char name;

}

5.     Package

It should be a lowercase letter such as java, lang.
If the name contains multiple words, it should be separated by dots (.) such as java.util, java.lang.

Example :

Package com.abc.xyz;

Class employee

{

//code

}

 

6.     Constant

It should be in uppercase letters such as RED, YELLOW.

If the name contains multiple words, it should be separated by an underscore(_) such as MAX_PRIORITY.

It may contain digits but not as the first letter.

Example :

Class Employee

{

//constant

Static final int MIN_Age = 18;

//code

}

Object and class Example:

Public class Student {

Int id ;

String name;

Public static void main (String[] args)

{

Student s1 = new Student();

System.out.println(s1.id);

System.out.println(s1.name);

}

}

Syntax of class :

Class <class_name>{

Field;

Method;

}

 

Class Student {

Int rollno;

String name;

Void insertRecord(int r, String n)

{

Rollno = r;

Name = n;

}

Void display()

{

System.out.println(rollno+ “ “ +name);

}

Class StudentTest {

Public static void main (String[] args)

{

Student s1 = new student();

Student s2 = new Student();

S1.insertRecord(101, “Ram”);

S2.insertRecord(102, “Sita”);

S1.display();

S2.display();

}

}

 

Class Student {

Int id;

String name;

}

Class StudentTest {

Public static void main (String arg[])

{

Student s1 = new Student();

Student s2 = new student();

S1.id = 101;

S1.name = “Ram”;

S2.id = 102;

S2.name = “Sita”;

System.out.println(s1.id+ “ “ s1.name);

System.out.println(s2.id+ “ “ s2.name);

}

}